Natural Organic–Inorganic Composite Hydrogel Electrolyte Enabling Efficient Ion Sieving for Stable Zinc–Iodine Batteries

Aqueous zinc‐iodine (Zn–I ₂ ) batteries have attracted considerable attention owing to their high energy density and intrinsic safety. However, challenges such as polyiodide shuttling, side reactions, and Zn dendrite growth hinder their further deployment. Herein, a composite hydrogel electrolyte composed of a sodium alginate (SA) matrix and halloysite nanotubes (HNTs) as the reinforcing component is rationally designed via a cation‐induced crosslinking strategy. The SA matrix, which is rich in hydrophilic functional groups, exhibits strong Zn ²⁺ affinity and I ₃ ⁻ repulsion. Furthermore, the oppositely charged inner and outer surfaces of one‐dimensional HNTs endow the hydrogel with fast and selective Zn ²⁺ transport pathways, leading to high ion conductivity (22.32 mS cm ⁻¹ ) and transference number ( = 0.67). The synergistic ion‐regulation strategy ensures uniform Zn ²⁺ flux and efficient I ₃ ⁻ fixation. Thereby, the Zn anode demonstrates an ultralong plating/stripping life of 1100 h. Moreover, the Zn–I ₂ cells with the composite hydrogel electrolyte retain a high capacity of 122.1 mAh g ⁻¹ after 5000 cycles at 4 A g ⁻¹ (capacity retention of 86.7%). The proposed approach enables the facile fabrication of functional hydrogels from earth‐abundant minerals and polymers, offering a sustainable solution for aqueous Zn–I ₂ batteries.